#include <iostream>
#include <vector>

using namespace std;

int main(){
  int n;cin>>n;
  vector<int> A(n);
  int nw = 0;
  for(int i = 0; n > i; i++){
    cin>>A[i];
    nw ^= A[i];
  }
  if(nw != 0){
    cout << 1 << endl;
    for(int i = 0; n > i; i++){
      if(A[i] >= nw){
        cout << i+1 << " " << nw << endl;
        A[i] -= nw;
        break;
      }
    }
    int ret;cin>>ret;
    if(ret == -1)return 0;
  }else{
    cout << 0 << endl;
  }
  
  while(true){
    int i,k;cin>>i>>k;
    A[i-1] -= k;
    int ret;cin>>ret;
    if(ret == -1)return 0;
    for(int j = 0; n > j; j++){
      if(A[j] >= nw && (A[j]^(A[j]-k)) == k){
        cout << j+1 << " " << k << endl;
        A[j] -= nw;
        break;
      }
    }
    cin>>ret;
    if(ret == -1)return 0;
  }
}